1. Field of the Invention
The present invention is generally related to a key operated door interlock switch mechanism and, more particularly, to an interlock switch that utilizes a cam structure comprising two cams that interact with a key that comprises two actuator portions.
2. Description of the Prior Art
Many different types of key interlock switches are known to those skilled in the art. Interlock switches can be used to assure that a certain condition is satisfied before a machine is permitted to operate. For example, a protective door may be employed to prevent a human operator from being harmed during the operation of a machine. To assure that the arms or hands of an operator are not within a dangerous zone of a machine during its activation, a switch is often incorporated as part of the protective door and the switch prevents the machine from being operated unless the door is closed. As an example, a key may be attached to the movable portion of a door and an associated switch structure can be associated with the stationary part of the protective housing around a machine.
Many types of door interlock switches are susceptible to human interference or tampering. In other words, an operator may take steps to either disarm the protective mechanism or defeat its protective characteristics. Many different types of door interlock switches have been developed to discourage or completely prevent this type of tampering.
Berthaud et al U.S. Pat. No. 4,904,829, which issued on Feb. 27, 1990, discloses an actuator controlled key lock switch that attaches a key to the door of an electrical equipment cubical. The key is capable of sliding within a passage way to as to cause pivotable displacement of a cam and upward displacement of a push rod, thus releasing a switch lug. A locking rod forming part of a slide block which is coupled with the push rod is capable of moving between a locking position in which an annular channel permits displacement of the key and an unlocking position in which the locking rod is engaged within a key notch. One end of the slide block projects from the top face of the switching unit head in order to be downwardly displaced by an actuator, where upon the key can be withdrawn without difficulty or danger.
Rapp et al U.S. Pat. No. 4,454,392, which issued on Jun. 12, 1984, describes a safety switch that comprises a drive and locking device. A key is used to operate the drive. The drive comprises a ram longitudinally moved by the key. The locking device includes a blocking member for the ram which can only be released by the key.
Bochard et al U.S. Pat. No. 4,695,684, which issued on Sep. 22, 1987, discloses an electric safety switch that can only be actuated by means of a key carried by a movable part of an installation. With its ramp, the key causes retraction of a bolt which is carried by a dividing wall of a rotary sector and, with its finger causes the angular driving of a groove of this dividing wall, the latter element entirely covering the cam surfaces which actuate the switch pusher. These switches are advantageously used in installation such as elevators and in safety circuits associated with cabinet doors.
Eicker et al U.S. Pat. No. 4,395,608, which issued on Jul. 26, 1983, describes a safety switch assembly in which an electrical interlock comprises a switch that is operated by a rotatable cam member coupled to the movable switch contacts by a longitudinally movable slider. Rotation of the cam member, which is contained within the same housing as the switch contacts, is caused by engagement, in slots in the periphery of the cam member, of an actuator mounted for movement relative to the switch housing.
Interlock switches, by their nature, must be sufficiently sophisticated to inhibit tampering. However, this level of sophistication often increases the manufacturing and assembly costs of the switch. It would therefore be significantly beneficial if an interlock switch could be provided which is appropriately sophisticated for the purpose of defeating an attempt to tamper with the switch, but able to be manufactured at a reduced cost. In addition, it would be advantageous if a switch of this type were able to be made in such a way that minor alterations to the switch, during manufacturing, could discriminate between various keys of generally similar design. This feature would enable the interlock switches to operate in the manner of normal door locks wherein a particular switch could only be operated by a particular key even though the general operation and interrelationship between the locks and keys are generally similar in all cases.